This invention relates to a case or container for housing a pressure gauge movement. More specifically, this invention relates to a case construction which utilizes a rather simple and economical apparatus for mounting a viewing window.
It is well known in the art that pressure gauges frequently use a Bourdon tube to convert the fluid or gas pressure into an observable needle or pointer movement, references to a graduated dial. These pressure gauges often are filled with oil to dampen pointer vibration. A Bourdon tube can rupture and raise the pressure in the case and thereby dislodge the viewing window. To prevent a pressure build-up in the case, pressure release devices are used, such as a blow-off safety back (shown herein), an expandable, diaphramatic case back or a pressure release valve.
Since the case intended for this type of application may be oil filled, the viewing window should be in a fluid sealing relation to the case end and should not dislodge before the pressure release functions. Furthermore, the arrangement employed for retaining the viewing window should facilitate easy removal of the window for access to the gauge movement for calibration (zeroing) and repair. In addition, the apparatus or arrangement should facilitate easy and economical assembly of the complete pressure gauge. Lastly, special tools or machinery should not be required to assemble and disassemble the complete gauge.
It can be observed that various techniques for mounting a viewing window on a gauge case are disclosed in the prior art. In general, screws or somewhat complicated collar arrangements are employed which may necessitate the use of special tools or machinery for mounting and dismounting the viewing window. For example, in FIG. 4 of U.S. Pat. No. 3,370,470, the ring 26, which consists of a thin copper sheet, is positioned along the sidewall 2 of the gauge case so as to press the window or disc against a resilient gasket. With disc 17 thus placed against the gasket, ring 26 is bent into groove 25 on the sidewall 2 of the case. Solely for cosmetic purposes, a cover 19 is provided over ring 26, which is fastened to the case wall by a plurality of screws. It should be observed that mounting the viewing window in this manner requires the use of special tools to bend ring 26 into groove 25. It follows that to remove the viewing window, special tools are also required to unbend the ring from the groove, and it is likely that ring 26 will be distorted or deformed when removed and cannot be reused to remount the window.